.TH std::unordered_multimap::merge 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::unordered_multimap::merge \- std::unordered_multimap::merge

.SH Synopsis
   template< class H2, class P2 >
   void merge( std::unordered_map<Key, T, H2, P2, Allocator>& source  \fB(1)\fP \fI(since C++17)\fP
   );
   template< class H2, class P2 >
   void merge( std::unordered_map<Key, T, H2, P2, Allocator>&& source \fB(2)\fP \fI(since C++17)\fP
   );
   template< class H2, class P2 >
   void merge( std::unordered_multimap<Key, T, H2, P2, Allocator>&    \fB(3)\fP \fI(since C++17)\fP
   source );
   template< class H2, class P2 >
   void merge( std::unordered_multimap<Key, T, H2, P2, Allocator>&&   \fB(4)\fP \fI(since C++17)\fP
   source );

   Attempts to extract ("splice") each element in source and insert it into *this using
   the hash function and key equality predicate of *this.

   No elements are copied or moved, only the internal pointers of the container nodes
   are repointed. All pointers and references to the transferred elements remain valid,
   but now refer into *this, not into source. Iterators referring to the transferred
   elements and all iterators referring to *this are invalidated.

   The behavior is undefined if get_allocator() != source.get_allocator().

.SH Parameters

   source - compatible container to transfer the nodes from

.SH Return value

   \fI(none)\fP

.SH Complexity

   Average case O(N), worst case O(N * size() + N), where N is source.size().

.SH Example


// Run this code

 #include <iostream>
 #include <string>
 #include <unordered_map>
 #include <utility>

 // print out a std::pair
 template<class Os, class U, class V>
 Os& operator<<(Os& os, const std::pair<U,V>& p)
 {
     return os << '{' << p.first << ", " << p.second << '}';
 }

 // print out an associative container
 template<class Os, class K, class V>
 Os& operator<<(Os& os, const std::unordered_multimap<K, V>& v)
 {
     os << '[' << v.size() << "] {";
     bool o{};
     for (const auto& e : v)
         os << (o ? ", " : (o = 1, "")) << e;
     return os << "}\\n";
 }

 int main()
 {
     std::unordered_multimap<std::string, int>
         p{{"C", 3}, {"B", 2}, {"A", 1}, {"A", 0}},
         q{{"E", 6}, {"E", 7}, {"D", 5}, {"A", 4}};

     std::cout << "p: " << p << "q: " << q;

     p.merge(q);

     std::cout << "p.merge(q);\\n" << "p: " << p << "q: " << q;
 }

.SH Possible output:

 p: [4] {{A, 1}, {A, 0}, {B, 2}, {C, 3}}
 q: [4] {{A, 4}, {D, 5}, {E, 6}, {E, 7}}
 p.merge(q);
 p: [8] {{E, 6}, {E, 7}, {C, 3}, {A, 1}, {A, 0}, {A, 4}, {D, 5}, {B, 2}}
 q: [0] {}

.SH See also

   extract extracts nodes from the container
   \fI(C++17)\fP \fI(public member function)\fP
           inserts elements
   insert  or nodes
           \fI(since C++17)\fP
           \fI(public member function)\fP
